Because positron emission tomography is a mouthful, radiologists call it a PET scan for short.

Doctors often use the diagnostic exam often to detect cancer and measure the effects of cancer treatment. The test can also monitor blood flow to the heart and hunt for signs of coronary artery disease. In patients with memory disorders, doctors use PET scans of the brain to look for brain tumors that can be surgically removed.

Here's how it works. A nurse injects a patient with a radioactive substance that attaches to a compound in the body such as sugar, called glucose. The patient then lies down on an exam table and is passed through the PET scan, which looks like a large donut. Rings in the machine detect the emission of energy from the radioactive substance in the body.

The exam results in an image of different colors and brightness. Healthy tissue uses glucose for energy, which will appear on a PET image as a bright color. But cancerous tissue has higher levels of glucose, and attracts more of the radioactive substance, which appears as brighter colors on a PET image.

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Corey Binns

Corey Binns lives in Northern California and writes about science, health, parenting, and social change. In addition to writing for Live Science, she's contributed to publications including Popular Science, TODAY.com, Scholastic, and the Stanford Social Innovation Review as well as others. She's also produced stories for NPR’s Science Friday and Sundance Channel. She studied biology at Brown University and earned a Master's degree in science journalism from NYU. The Association of Health Care Journalists named her a Centers for Disease Control and Prevention Health Journalism Fellow in 2009. She has chased tornadoes and lived to tell the tale.